Tumordormancypresentsabarriertoeffectivetherapy.Tumordormancyisthoughttobecomprisedof threekeyelements:cellulardormancy,wheretumorcellsmaintainaquiescent,slow-cyclingstate,angiogenic dormancy, where the growth of the overall micro-metastasis is kept in check by apoptosis due to lack of vascularization, and immune-mediated dormancy, where the immune system continues to edit the tumor population, keeping it in equilibrium. The equilibrium of these dormant subpopulations is maintained until microenvironmental conditions favor their outgrowth. To date, it is unclear what those exact micro- environmentalconditionsare.Understandingwhytumorcellsleavethisdormantstateandbecomeaggressive isacriticalunmetneedincancerbiology.Oneindisputablefactabouttumordormancyisthatincaseswherea tumor is dormant, a significant lapse of time occurs between the diagnosis and removal of a primary tumor, andtherecurrenceofmetastasis.Duringthislapseoftime,anorganismages,andageisapoorprognostic factor for multiple tumor types, including melanoma. We hypothesize that changes in the aging microenvironment can contribute to an emergence from dormancy. Our long-term goal is to understand how theagedmicroenvironmentcontributestoanemergencefromdormancy. OurdataimplicatetheWntsignalingpathwayinmelanomadormancy.WehaveidentifiedWnt5AandsFRP2 (secretedfrizzledrelatedprotein2),astwoWntpathwaymodulatorswhoselevelandactivitywehypothesize play roles in the emergence from tumor dormancy. We have shown that aging accelerates melanoma metastasis,partlymediatedbyWnt5AandsFRP2,whichareincreasedduringaging.Ourdataindicatethat sFRP2 enhances angiogenesis, potentially regulating angiogenic dormancy. sFRP2-mediated angiogenesis has been shown to require endothelial cell expression of Wnt5A and we will test this in the context of tumor dormancy. Immune-mediated dormancy relies in part on the activity of myeloid derived suppressor cells (MDSCs),andtheirabilitytoregulateCD8+cells.OurdatashowthatMDSCsareincreasedintheagedtumor microenvironment,andfurther,thatMDSCsinthetumormicroenvironmentbegintoexpresstheirownWnt5A. Usingnovelanimalmodelswehavecreated,wewilltestthehypothesisthatnon-canonicalWntsignalingcan regulateimmune-mediateddormancyofmicrometastases,viaeffectsonangiogenesisandMDSCs.